The present invention relates to an apparatus for continuously producing a tube having helical grooves in its inner surface and useful chiefly as a refrigerant tube for heat exchangers.
Tubes having helical grooves in the inner surface, when used as refrigerant tubes, assure heat exchange between the refrigerant passing through the tube and the outside air with a higher efficiency than is achieved by usual tubes, so that these grooved tubes are advantageous for producing heat exchangers of reduced size with use of reduced quantities of materials. An apparatus for producing such a tube internally having helical grooves has already been proposed in Unexamined Japanese Patent Publication No. 212815/83. This conventional apparatus comprises a first drum, a cradle supporting the shaft of the first drum, a flier having an axis intersecting the axis of the first drum at right angles therewith and rotatable around the first drum, and a second drum. One of the two drums serves as a pay-off drum for paying off a tube having straight grooves in at least one of its inner and outer surfaces, while the other drum serves as a take-up drum for winding thereon the helically grooved tube obtained. With the rotation of the flier, the straight-grooved tube is twisted, whereby the straight grooves are deformed to helical grooves.
The conventional apparatus has the likelihood that when the tube is twisted, the torsion will be transmitted toward the pay-off drum. The torsion, if transmitted toward the pay-off drum, produces variations in the twist angle of the grooves and hinders smooth tube paying-off operation. Further if the tube has an eccentric wall and is twisted, it is likely that the tube will become deformed or flattened.